Estimating measures to reduce the transmission of SARS-CoV-2 in Australia to guide a ‘National Plan’ to reopening

Background In mid-2021, widespread availability of COVID-19 vaccines with demonstrated impacts on transmission promised relief from the strict public health and social measures (PHSMs) imposed in many countries to limit spread and burden. We were asked to define vaccine coverage thresholds for transition through the stages of Australia’s ‘National Plan’ to easing restrictions and reopening international borders. Methods Using available evidence of vaccine effectiveness against the then-circulating Delta variant, we used a mathematical model to determine vaccine coverage targets. The absence of any COVID-19 infections in many sub-national jurisdictions in Australia posed particular methodological challenges for modelling in this setting. We used a novel metric called Transmission Potential (TP) as a proxy measure of the population-level effective reproduction number. We estimated TP of the Delta variant under a range of PHSMs, test-trace-isolate-quarantine (TTIQ) efficiencies, vaccination coverage thresholds, and age-based vaccine allocation strategies. Findings We found that high coverage of vaccination across all age groups (≤ 70%) combined with ongoing TTIQ and minimal PHSMs was sufficient to avoid strict lockdowns. At lesser coverage (≥ 60%) rapid case escalation risked overwhelming of the health sector and would prompt a need to reimpose strict restrictions, with substantive economic impacts in order to achieve the goals of the National Plan. Maintaining low case numbers was the most beneficial strategy for health and the economy, and at higher coverage levels (≥ 80%) further easing of restrictions was deemed possible. Interpretation These results reinforced recommendations from other modelling groups that some level of PHSMs should be continued to minimise the burden of the Delta variant following achievement of high population vaccine coverage. They directly informed easing of COVID-19 restrictions in Australia. Funding This study was supported by the Australian Government Department of Health and Ageing, and the National Health and Medical Research Council’s Centre of Research Excellence scheme (GNT1170960). ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was directly funded by the Australian Government Department of Health Office of Health Protection. Additional support was provided by the National Health and Medical Research Council of Australia through its Centres of Research Excellence (SPECTRUM, GNT1170960) and Investigator Grant Schemes (JMcV Principal Research Fellowship, GNT1117140; FMS Emerging Leader Fellowship, 2021/GNT2010051) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Code to reproduce these analyses are available at, ; Code to create figures 3 and S1 can be found in . This code uses outputs from regular situational assessment work described in that are conducted using data provided under confidential agreement from the Australian Commonwealth Government.